Isocyanatosilanes are well-known silicon-containing materials which have long been used in the production of other silicon-containing products such as in the production of polyurethanes, e.g., polyurethanes used in the building and construction fields. Unfortunately, isocyanatosilanes tend to have a high manufacturing cost, which limits their potential applications. For instance, 3-isocyanatopropylalkoxysilanes are used as end-cappers in the preparation of silylated polymers. Even though 3-isocyanatopropylalkoxysilanes are used in small quantities, their high cost significantly increases the total cost of silylated polymers and the products made from them. Various methods are known for preparing isocyanatosilanes, all of which suffer from drawbacks that result in a high cost or other undesired features of the produced isocyanatosilanes. Such known methods of making isocyanatosilanes include:
1. Formation of isocyanatosilane by the thermal cleavage (or cracking) of a carbamatosilane (along with formation of the by-product alcohol);
2. Formation of isocyanatosilane via the reaction of haloalkylsilane with metal cyanate;
3. Formation of isocyanatosilane via the reaction of aminosilane with phosgene:
4. Formation of isocyanatosilane via the hydrosilylation of allyl isocyanate with hydridosilane.
Method 1 typically involves multiple steps to first prepare the carbamatosilane, followed by the relatively inefficient cracking of the carbamate into isocyanatosilane.
Method 2 has the drawback of low yields of isocyanatosilane when the reaction is performed due to significant trimerization of the formed isocyanatosilane, resulting in the formation of by-product isocyanurate.
Method 3 involves the handling of dangerous phosgene gas and requires the efficient scavenging of acid by-products formed during the course of the reaction.
Method 4 has been unattractive due to low yields, high reaction temperature, long reaction time and the formation of unwanted by-products.
There thus remains a desire in the industry for a process for the synthesis of isocyanatosilanes yielding the target molecules in high yield, without major by-products, such as cyanurates or undesired high molecular weight species, based on large scale and economically accessible raw materials, and avoiding the use of regulated compounds, such as phosgene.